Visible light catalyst, method for preparing the same, and use thereof

Abstract

The application discloses a visible light catalyst and a preparation method thereof. Firstly, ZnFe2O4 nanoparticles are prepared by a liquid phase mixing-evaporating solvent-calcining method; then the ZnFe2O4 nanoparticles are uniformly dispersed in an aqueous solution containing different mass of glucose, the glucose is converted into hydrothermal carbon (HC) through a hydrothermal reaction, and the HC is combined with the ZnFe2O4 nanoparticles to obtain a series of HC / ZnFe2O4 nanocomposites. The method is simple and easy to implement, raw materials are easy to obtain, and the cost is low; the nanocomposite has high visible light catalytic activity on the reduction of bromate and hexavalent chromium in water, and can be applied to treating bromate and hexavalent chromium pollutants in water as a new visible light catalyst.

Description

Technical Field

[0001] This invention belongs to the field of photocatalyst materials technology, specifically relating to a visible light photocatalyst (HC / ZnFe2O4 nanocomposite material) for treating bromate and hexavalent chromium pollutants in water and its preparation method. Background Technology

[0002] Water pollution has become an increasingly serious problem worldwide. Improper treatment of industrial wastewater, agricultural runoff, and sewage is the main cause. Treating pollution in drinking water sources is a crucial measure concerning human health and safety. Ozone oxidation technology, due to its advantages such as high organic matter removal efficiency, low cost, and simple operation, has been widely used in drinking water disinfection. However, natural drinking water resources typically contain 2-293 μg / L of bromide ions (Br₂). − ), can be oxidized by ozone to bromate ions (BrO3). − BrO3 − It is carcinogenic and genotoxic, and has been classified as a Group 2B carcinogen by the World Health Organization. Therefore, many authoritative organizations have raised concerns about the presence of BrO3 in drinking water. − The concentration must not exceed 10 μg / L.

[0003] Removal of BrO3 − The methods can be roughly divided into three categories: (1) Removing Br from water before ozone disinfection − (2) Inhibit Br during ozone disinfection − To BrO3 − (3) Removal of BrO3 from ozone-disinfected water − The first two methods are limited in practical applications due to their low efficiency, high cost, and complex operation. The third method includes ultraviolet irradiation, electrolysis, adsorption, ion exchange, and photocatalytic reduction. Among these, semiconductor photocatalysis is a green, efficient, and low-cost method for reducing BrO3. − The reduction treatment method is more sustainable and has better development prospects.

[0004] Chromium salts are an important class of inorganic chemical products and a crucial raw material for my country's national economic development. Statistics show that chromium salts are related to over 10% of my country's commodity products. Currently, my country is the world's largest producer and consumer of chromium salts. With future economic development, the corresponding demand for chromium salts will steadily increase. However, the production and use of chromium salts generate large amounts of hexavalent chromium (Cr(VI)) wastewater. Cr(VI) is characterized by high toxicity, high water solubility, and strong migration, seriously endangering the environment and human health, and is a priority pollutant controlled in my country. Therefore, industrial wastewater containing Cr(VI) must undergo treatment to meet standards before discharge. Because Cr(III) has low toxicity and readily forms Cr(OH)3 precipitate (the solubility product constant of Cr(OH)3 is 6.3 × 10⁻⁶), further treatment is necessary. -31 Therefore, a common method for treating Cr(VI) wastewater is to add a reducing agent to reduce Cr(VI) to Cr(III). However, traditional chemical reduction methods consume large amounts of reducing agent, resulting in high treatment costs and a high risk of introducing secondary pollution. Photocatalytic reduction based on solar energy utilization and conversion offers economic and environmental advantages for treating Cr(VI) wastewater.

[0005] However, existing photocatalyst materials have low visible light catalytic activity and high cost, which cannot meet the requirements of industrial applications. Therefore, to realize the widespread application of photocatalysis in the treatment of bromate and hexavalent chromium pollutants in water, it is necessary to develop efficient and low-cost visible light photocatalysts.

[0006] ZnFe₂O₄ is a low-cost, non-toxic, stable, and visible-light-responsive semiconductor material with promising applications. Currently, the main methods for preparing ZnFe₂O₄ are high-temperature solid-state reaction and solvothermal methods. However, the high-temperature solid-state reaction method not only requires high temperatures (>800℃) and consumes a lot of energy, but also produces products with large particle sizes, small specific surface areas, and low photocatalytic activity. The solvothermal method, on the other hand, has limited single-batch synthesis yields and low production efficiency, making it unsuitable for large-scale production. Furthermore, when ZnFe₂O₄ is used alone as a photocatalyst, it suffers from rapid photo-generated charge recombination rates and low separation efficiency.

[0007] Therefore, it is both necessary and meaningful to develop a simple, efficient, and scalable method for preparing ZnFe2O4 nanoparticles and to perform composite modification on the prepared ZnFe2O4 nanomaterials to suppress the recombination of photogenerated charges, thereby enabling them to have high visible light photocatalytic activity. Summary of the Invention

[0008] Objective: To address the shortcomings of existing technologies, this invention provides a visible light photocatalyst capable of treating both bromate pollutants in water and hexavalent chromium wastewater, along with its preparation method. The prepared HC / ZnFe2O4 nanocomposite material exhibits high visible light photocatalytic activity, thus solving one or more of the aforementioned problems in the prior art.

[0009] Technical solution: To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0010] A method for preparing a visible light photocatalyst, comprising:

[0011] ZnFe2O4 nanoparticles were first obtained using a liquid-phase mixing-solvent evaporation-calcination method.

[0012] Then, ZnFe2O4 nanoparticles were uniformly dispersed in an aqueous solution containing different masses of glucose. The glucose was converted into hydrothermal carbon through a hydrothermal reaction and then combined with ZnFe2O4 nanoparticles to obtain a series of HC / ZnFe2O4 nanocomposites.

[0013] Synthesis of ZnFe2O4 nanoparticles: Deionized water was used as the solvent, and zinc nitrate, ferric nitrate, and citric acid were added and stirred until dissolved. The resulting mixture was heated at 90°C for 12 h to obtain a red gel. The gel was further calcined in a muffle furnace at 450°C for 4 h, and then ground to obtain ZnFe2O4 nanoparticles.

[0014] Furthermore, in the above reaction, the molar ratio of zinc nitrate, ferric nitrate, and citric acid is 1:2:4; the reaction temperature in the muffle furnace is 450℃, and the reaction time is 4 h.

[0015] Synthesis of HC / ZnFe2O4 nanocomposites: Different masses of glucose were dissolved in deionized water, and then ZnFe2O4 nanoparticles were added to disperse them evenly. The mixture was then reacted in a high-pressure reactor at 180℃ for 10 h. After natural cooling to room temperature, the resulting precipitate was centrifuged, washed, and dried to obtain a series of HC / ZnFe2O4 nanocomposites.

[0016] Furthermore, in the above reactions, the mass ratio of glucose to ZnFe2O4 added was 1:100, 5:100, and 10:100. The reaction was carried out in an oven at 180°C for 10 h.

[0017] More specifically, it includes the following steps:

[0018] 1) Synthesis of ZnFe2O4 nanoparticles: 5 ml of deionized water was placed in a 50 ml beaker, and 2.5 mmol of zinc nitrate, 5 mmol of ferric nitrate, and 10 mmol of citric acid were weighed and added to the beaker. After stirring for 15 min, the mixture was heated in an oven at 90 °C for 12 h to obtain a red gel. The gel was transferred to a 20 ml crucible and calcined in a muffle furnace at 450 °C for 4 h. After calcination, the ZnFe2O4 nanoparticles were obtained.

[0019] 2) Synthesis of HC / ZnFe2O4 nanocomposite material: 10 mg, 50 mg and 100 mg of glucose were weighed and dissolved in 50 ml of deionized water, and then 1000 mg of the synthesized ZnFe2O4 nanoparticles were added. The mixture was stirred for 30 min to disperse it evenly. The mixture was then transferred to a 100 ml stainless steel high-pressure reactor lined with polytetrafluoroethylene, sealed, and placed in an oven at 180 °C for 10 h. After natural cooling to room temperature, the precipitate was centrifuged, washed and dried to obtain the HC / ZnFe2O4 nanocomposite material.

[0020] The preparation method of this invention has the following advantages: the ZnFe2O4 particles synthesized by the liquid-phase mixing-solvent evaporation-calcination method have small size (10-25 nm) and large specific surface area; the method for preparing HC / ZnFe2O4 nanocomposites of this invention is simple and easy to implement, the raw materials are readily available, and the cost is low; the product prepared by this invention has higher visible light photocatalytic activity than ZnFe2O4 in treating bromate and hexavalent chromium pollutants in water. Therefore, the HC / ZnFe2O4 visible light photocatalyst prepared by this invention can be used for the efficient treatment of bromate and hexavalent chromium pollutants in water.

[0021] Furthermore, in step 1) of this invention, the molar ratio of zinc nitrate, ferric nitrate, and citric acid is 1:2:4; the reaction temperature in the muffle furnace is 450°C, and the reaction time is 4 h. The design aims to ensure that the reactants react completely, and the product is pure-phase, small-particle-size ZnFe2O4 nanoparticles.

[0022] In step 2), the mass ratio of glucose to ZnFe2O4 added is 1:100, 5:100, or 10:100. The rationale behind this design is that if the mass ratio of glucose to ZnFe2O4 is less than 1 / 100, the photogenerated charge transfer and separation of the composite material are limited, and the photocatalytic activity cannot be effectively improved; if the mass ratio of glucose to ZnFe2O4 is greater than 10 / 100, the glucose carbonization easily completely coats the catalyst, reducing the contact between the reactants and the photocatalytic active sites, thus lowering the photocatalytic activity.

[0023] In step 2), the reaction temperature is 180℃ and the reaction time is 10 h. The rationale behind this design is that if the reaction temperature is too low or the time is too short, glucose carbonization will be insufficient, resulting in less hydrothermal carbon that cannot fully recombine with ZnFe2O4. If the reaction temperature is too high or the time is too long, oxygen-containing functional groups such as hydroxyl and carboxyl groups on the surface of the hydrothermal carbon may desorb or decompose, leading to a reduction in active sites on the material surface. Both of these possibilities are detrimental to significantly improving the visible light photocatalytic activity of the composite material.

[0024] On the other hand, the present invention also provides a visible light catalyst, wherein the visible light catalyst is an HC / ZnFe2O4 nanocomposite material, which is prepared by the above-mentioned method for preparing a visible light catalyst for treating bromate and hexavalent chromium pollutants in water.

[0025] On the other hand, the present invention also provides the application of the visible light catalyst in the treatment of bromate and hexavalent chromium contaminants in water.

[0026] Carbon materials typically possess large specific surface areas, strong pollutant adsorption capabilities, and good electrical conductivity, and can be well composited with most inorganic semiconductor materials. Therefore, modification with carbon materials can often significantly improve the photocatalytic activity of inorganic semiconductors. However, currently, most carbon materials used for composite modification of inorganic semiconductor photocatalysts are relatively expensive, such as graphene and its derivatives, carbon nanotubes, and carbon quantum dots. Hydrothermal carbon (HC) not only possesses typical carbon material characteristics but also has advantages such as simple synthesis, environmental friendliness, readily available raw materials, and low cost. Furthermore, it exhibits semiconductor properties, effectively absorbs visible light, and can form heterojunctions with inorganic semiconductors with large contact areas. Therefore, using hydrothermal carbon to composite modify ZnFe2O4 can suppress the recombination of photogenerated charges, prolong the lifetime of photogenerated electrons and holes, and thus improve its photocatalytic efficiency.

[0027] Beneficial Effects: The visible light photocatalyst and its preparation method provided by this invention have the following advantages: the ZnFe2O4 particles synthesized by the liquid-phase mixing-solvent evaporation-calcination method have small particle size (10-25 nm) and large specific surface area; the method for preparing HC / ZnFe2O4 nanocomposites by this invention is simple and easy to implement, the raw materials are readily available, and the cost is low; the product prepared by this invention exhibits higher visible light photocatalytic activity than ZnFe2O4 in treating bromate and hexavalent chromium pollutants in water. Therefore, the HC / ZnFe2O4 visible light photocatalyst prepared by this invention can be used for the efficient treatment of bromate and hexavalent chromium pollutants in water. Attached Figure Description

[0028] Figure 1 The XRD patterns of the products (ZnFe2O4 and HC / ZnFe2O4) prepared in Example 1 are shown below.

[0029] Figure 2 The FTIR spectra of the products (ZnFe2O4 and HC / ZnFe2O4) prepared in Example 1 are shown below.

[0030] Figure 3 XPS images of the products (ZnFe2O4 and HC / ZnFe2O4) prepared in Example 1.

[0031] Figure 4 TEM images of the products (ZnFe2O4 and HC / ZnFe2O4) prepared in Example 1;

[0032] Figure 5 The product prepared in Example 1 under visible light irradiation under photocatalytic reduction of BrO3. − Activity evaluation diagram (C) i0 =BrO3 in the solution at the start of light exposure − Concentration, C it = BrO3 in the solution after t minutes of light exposure − concentration);

[0033] Figure 6 The graph shows the photocatalytic reduction activity of the product prepared in Example 1 under visible light irradiation (C). i0 = The concentration of Cr(VI) in the solution at the start of light exposure, C it = The concentration of Cr(VI) in the solution after t minutes of illumination. Detailed Implementation

[0034] The present invention will be further described below with reference to embodiments. The following embodiments are only used to illustrate the performance of the present invention more clearly, and should not be limited to the embodiments described below.

[0035] Example 1

[0036] I. Synthesis of HC / ZnFe2O4 composite material:

[0037] 1) Synthesis of ZnFe2O4 nanoparticles: 5 ml of deionized water was measured into a 50 ml beaker, and 2.5 mmol of zinc nitrate, 5 mmol of ferric nitrate, and 10 mmol of citric acid were weighed and added to the beaker. After stirring for 15 min, the mixture was heated in an oven at 90 °C for 12 h to obtain a red gel. The gel was transferred to a 20 ml crucible and calcined in a muffle furnace at 450 °C for 4 h. After calcination, the ZnFe2O4 nanoparticles were obtained by grinding.

[0038] 2) Weigh 50 mg of glucose and dissolve it in 50 ml of deionized water. Then add 1000 mg of the synthesized ZnFe2O4 nanoparticles and stir for 30 min to disperse them evenly. Transfer the mixture to a 100 ml stainless steel high-pressure reactor lined with polytetrafluoroethylene, seal it, and place it in an oven to heat at 180°C for 10 h. Allow it to cool naturally to room temperature. Centrifuge, wash, and dry the resulting precipitate to obtain the HC / ZnFe2O4 nanocomposite material.

[0039] The phases were analyzed using a Rigaku Ultima IV X-ray diffractometer (XRD) from Japan. Figure 1 As shown, the results indicate that the X-ray diffraction peaks of the product prepared in Example 1 match those of the standard card (JCPDS Card No. 82-1042), classifying it as cubic spinel-type ZnFe2O4. Due to the low content and poor crystallinity of hydrothermal carbon, no diffraction peaks of hydrothermal carbon were observed in the XRD pattern of HC / ZnFe2O4.

[0040] The composition (chemical bonds or functional groups) was analyzed using a Thermo Fisher Scientific Antaris II Fourier transform near-infrared spectrometer. Figure 2 As shown, the results indicate that the infrared spectrum of HC / ZnFe2O4 not only contains Fe-O of ZnFe2O4 (557 cm⁻¹), but also... -1 ), and contains C=C (1637cm) -1 ) and C=O (1677cm) -1 This indicates that HC / ZnFe2O4 is composed of ZnFe2O4 and HC.

[0041] The surface chemical composition was analyzed using an ESCALAB 250Xi X-ray photoelectron spectroscopy system from Thermo Scientific, USA. For example... Figure 3 As shown, the results indicate that all products prepared in Example 1 contain Zn. 2+ Fe 3+ O 2− While both contain carbon (C), the C content in HC / ZnFe2O4 is 2.25%, which is higher than the C content in ZnFe2O4 (1.67%, mainly due to adsorbed C-containing pollutants); this indicates that ZnFe2O4 and HC have successfully combined.

[0042] The morphology and size of the samples were observed using a Philips Tecnai 12 transmission electron microscope (PSE). Figure 4 As shown in (a) and (b), the results indicate that both ZnFe2O4 and HC / ZnFe2O4 are composed of nanoparticles with a size of 10-25 nm.

[0043] II. Study on the photocatalytic performance of the prepared products:

[0044] The performance of the prepared product in photocatalytic reduction of bromate and hexavalent chromium in water was evaluated using a GHX-2 photocatalytic instrument (excitation wavelength greater than 420 nm) customized by Yangzhou University City Science and Education Instrument Co., Ltd. The concentration of residual bromate in the solution at different reaction times was determined by the Ponceau S bleaching spectrophotometric method. The concentration of residual hexavalent chromium in the solution at different reaction times was determined by the diphenylcarbazide spectrophotometric method. The photocatalytic experimental results are as follows: Figure 5 and 6 As shown: The results indicate that the HC / ZnFe2O4 product prepared in Example 1 of this invention has high visible light photocatalytic activity for the reduction of bromate and hexavalent chromium in water, and its photocatalytic activity (photocatalytic reaction rate constant) is about 2.1 times that of ZnFe2O4.

[0045] This invention successfully prepared an HC / ZnFe2O4 visible light photocatalyst material with high visible light photocatalytic activity. From the above-described implementation steps and data analysis, the preparation method of this invention has the following advantages: the ZnFe2O4 particles synthesized by the liquid-phase mixing-solvent evaporation-calcination method have small particle sizes (10-25 nm) and large specific surface areas; the method for preparing the HC / ZnFe2O4 nanocomposite material is simple and easy to implement, the raw materials are readily available, and the cost is low; the product prepared by this invention exhibits higher visible light photocatalytic activity than ZnFe2O4 in treating bromate and hexavalent chromium pollutants in water. Therefore, the HC / ZnFe2O4 visible light photocatalyst prepared by this invention can be used for the efficient treatment of bromate and hexavalent chromium pollutants in water.

[0046] The present invention has been disclosed above with reference to preferred embodiments, but it is not intended to limit the present invention. All technical solutions obtained by equivalent substitution or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A method for preparing a visible light photocatalyst, characterized in that, include: ZnFe2O4 nanoparticles were first prepared by liquid-phase mixing-solvent evaporation-calcination method; Then, ZnFe2O4 nanoparticles were uniformly dispersed in an aqueous solution containing different masses of glucose. The glucose was converted into hydrothermal carbon (HC) through a hydrothermal reaction and then combined with ZnFe2O4 nanoparticles to obtain a series of HC / ZnFe2O4 nanocomposites.

2. The method for preparing the visible light photocatalyst according to claim 1, characterized in that, Synthesis of ZnFe2O4 nanoparticles: Using deionized water as a solvent, zinc nitrate, ferric nitrate and citric acid were added and stirred to dissolve them. The resulting mixture was heated at 90°C for 12 h to obtain a red gel. The gel was further calcined in a muffle furnace at 450°C for 4 h, and then ground to obtain ZnFe2O4 nanoparticles.

3. The method for preparing the visible light photocatalyst according to claim 2, characterized in that, The molar ratio of zinc nitrate, ferric nitrate, and citric acid added is 1:2:

4.

4. The method for preparing the visible light photocatalyst according to claim 2, characterized in that, The reaction temperature in the muffle furnace was 450℃, and the reaction time was 4 h.

5. The method for preparing a visible light photocatalyst according to claim 1, characterized in that, Synthesis of HC / ZnFe2O4 nanocomposite materials: Different masses of glucose were weighed and dissolved in deionized water, and then the prepared ZnFe2O4 nanoparticles were added to disperse them evenly. The mixture was then reacted in a high-pressure reactor at 180℃ for 10 h, and naturally cooled to room temperature. The resulting precipitate was washed and dried to obtain the HC / ZnFe2O4 nanocomposite material.

6. The method for preparing the visible light photocatalyst according to claim 5, characterized in that, The mass ratio of added glucose to ZnFe2O4 was 1:100, 5:100, and 10:

100.

7. The method for preparing a visible light photocatalyst according to claim 5, characterized in that, The reaction was carried out at 180°C in an oven for 10 h.

8. The method for preparing the visible light photocatalyst according to claim 1, specifically comprising the following steps: 1) Synthesis of ZnFe2O4 nanoparticles: 5 ml of deionized water was measured into a 50 ml beaker, and 2.5 mmol of zinc nitrate, 5 mmol of ferric nitrate, and 10 mmol of citric acid were weighed and added to the beaker. After stirring for 15 min, the mixture was heated in an oven at 90 °C for 12 h to obtain a red gel. The gel was transferred to a 20 ml crucible and calcined in a muffle furnace at 450 °C for 4 h. After calcination, the gel was removed and ground to obtain ZnFe2O4 nanoparticles. 2) Synthesis of HC / ZnFe2O4 nanocomposite material: 10 mg, 50 mg and 100 mg of glucose were weighed and dissolved in 50 ml of deionized water, and then 1000 mg of the synthesized ZnFe2O4 nanoparticles were added. The mixture was stirred for 30 min to disperse it evenly. The mixture was then transferred to a 100 ml stainless steel high-pressure reactor lined with polytetrafluoroethylene, sealed, and placed in an oven at 180 °C for 10 h. After natural cooling to room temperature, the precipitate was centrifuged, washed and dried to obtain the HC / ZnFe2O4 nanocomposite material.

9. A visible light photocatalyst, characterized in that, The visible light catalyst is an HC / ZnFe2O4 nanocomposite material, prepared by the visible light catalyst preparation method described in claims 1-8.

10. The use of the visible light catalyst of claim 9 in the treatment of bromate and hexavalent chromium contaminants in water.

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